The manufacture of electronic circuits for use in computers and similar devices includes deposits of electronic circuit lines, elements and traces onto ceramic sheets. The ceramic sheet is the substrate for the circuits and provides insulation between adjacent electrical paths, while at the same time provides a rigid support. A multi-layer structure of ceramic, each layer having electronic circuits formed and deposited on the layer, permits an inherently more compact and efficient structure. In the manufacture of these electronic devices, after the unfired ceramic substrate is formed, small holes are punched which extend from one face of the ceramic layer through the sheet to a second face of the ceramic layer. These holes are commonly known as via holes, and they permit the formation of electrically conductive paths from one face of the device to the second face which provide connections with electronic circuits on the second face or for connection to electronic circuits on an adjacent ceramic layer. In addition, the via hole may provide an electronic connection or path to another via hole on the next adjacent layer extending therethrough to connect to yet another layer in the multi-layer structure. In a multi-layer ceramic structure via holes are required to be very precisely positioned since they must match either with via holes in the next adjacent layer or must match with the precise location of an electrical contact on the next adjacent ceramic layer.
The formation of the holes in the ceramic material is accomplished in its green state. The green state of the ceramic layers exists prior to the sheets being fired and ceramic particles being fused. Prior to being fired, the green sheets are easily deformed therefore, the precision with which the via holes are formed into the green sheets is greatly dependent upon the use of apparatuses which minimizes distortion or disruption to the structural integrity of the green sheet, other than forming the via hole.
With the size of electrical components constantly being reduced, through technical improvement, the positioning of the via holes in ceramic green sheets is becoming ever more restrictive. Further, with the increase in the quantity of electronic circuits that may be positioned and packaged on a small area of a ceramic substrate, the requirement for a larger number of via holes is evident.
Large numbers of holes must be punched into a green sheet with a high degree of precision in order to properly position the holes; and at the same time, this punching operation must occur very rapidly in order to produce the large numbers of green sheets that are necessary in the mass production of electronic chip carriers. The fabrication of dedicated punches for certain fixed patterns of via holes is not practical because the same apparatus may be used to form different via hole patterns in ceramic green sheets being used for a large number of diverse electronic applications.
With the requirement for high speed and versatility of the hole positions, it becomes necessary to package a large number of punching devices into a relatively small area in order to maximize manufacturing throughput. Electrically controlled punches for punching holes in green sheets have been previously developed but the punches have some inherent disadvantages which are overcome by the present invention. The prior effort to create an electrically controlled punching mechanism to punch via holes into ceramic green sheets is reflected in U.S. Pat. No. 5,024,127, to Mueller et. al. Mueller shows an individual punch mechanism which utilizes a cylindrical magnet which extends over approximately half of the length of the punch mechanism. The magnet cylinder provides the magnetic field against which the voice coil operates, and the interaction of the magnetic fields between the cylindrical magnet and the voice coil acts to move the punch element. Punches of this general type have relatively weak magnetic fields and thus require a substantial electrical current to be passed through the voice coil in order to displace the punch and the punch cap. Further, the device of Mueller relies upon reversal of the magnetic forces generated by the voice coil to extract the punch from the green sheet. The relatively high level of electrical current, combined with the extended duty cycle of the voice coil, when used to retract the punch, results in substantial heat loads which must be dissipated to insure that the punch continues to operate properly.
While solenoids may be implemented in this type of punch, in order to generate sufficient forces and velocity for punching, the mass of the armature of the solenoid is so large that accelerations of sufficient magnitude to rapidly punch the ceramic green sheet with a minimum of distortion to the ceramic green sheet cannot be satisfactorily accomplished.
Since the punching power of solenoid actuated punches of this type and purpose generate relatively low levels of power in comparison to their size and electrical power requirements, and since it is desirable also to place as many punches as closely as possible in order to be able to accurately position via holes in ceramic green sheets, it is necessary to consider alternate designs for the propelling mechanism of the punch.